POSIX Compliance

Makar is not a UNIX system and does not claim SUS/POSIX conformance. It does, however, intentionally use a POSIX-shaped userspace model: Linux i386 syscall numbers where practical, static ELF programs, file descriptors, fork/exec/wait, signals, a small libc, and a shell that can run real scripts.

This page is written for application porters. It answers: what can a small C program rely on today, what is only a compatibility stub, and what still needs kernel work?

Current Headline

Makar currently supports:

• ring-3 ELF programs loaded by elf_exec
• fork, execve, wait4, getpid, getppid
• per-task file descriptor tables
• open, read, write, close, lseek, stat, fstat
• dup, dup2, pipe
• brk, userspace malloc, and anonymous mmap
• basic signal delivery and user signal handlers
• UTC time APIs
• x87/SSE FPU state saved/restored per task
• one-slot i386 TLS through set_thread_area
• dynamically-linked PIEs against a shared musl libc.so, loaded by musl’s own interpreter ld-musl-i386.so.1 (ET_DYN + PT_INTERP + full auxv)
• a userspace shell with pipes, redirection, list operators, background jobs, wait, quoting, and sh -c

It does not currently support:

• users, groups, permissions, or credentials
• process groups, sessions, or job-control terminal ownership
• pthreads or clone-style user threads
• networking or sockets
• a supported in-place JIT (tcc -run-style) execution model — TCC compiles to files and execs them instead
• complete Linux signal-mask semantics
• select, poll, or another fd readiness API
• a termios-compatible terminal interface

Process Model

Feature	Status	Notes
fork	Present	Copy-on-write page-directory clone via task_fork.
execve	Present	Replaces the current image with an ELF. envp is accepted but ignored.
wait4	Present	Supports WNOHANG; rusage is ignored.
exit	Present	Terminates the current task.
exit_group	Stub	Same as exit; Makar has one userspace thread per process.
getpid, getppid	Present	Expose task_t.pid and task_t.parent_pid.
set_tid_address	Stub	Returns the task pid for hosted libc startup.
vfork, posix_spawn	Absent	Native COW fork exists, so these are not currently needed.
clone, pthreads	Absent	No userspace thread groups.

PIDs are monotonic for the boot session. The idle task is pid 1. Task slots are reused internally after a task becomes TASK_DEAD, but pid values keep advancing.

File Descriptors and VFS

Feature	Status	Notes
fd table	Present	Each task has its own fd table.
stdin/stdout/stderr	Present	fd 0 = keyboard/stdin, fd 1 = terminal/stdout, fd 2 = terminal + serial/stderr.
open	Present	Supports common read/write/create/truncate/append flags; mode is ignored.
read, write	Present	File, pipe, terminal, and keyboard paths.
close	Present	Flushes dirty file buffers.
lseek	Present	SEEK_SET, SEEK_CUR, SEEK_END.
dup	Present	Allocates the lowest free fd.
dup2	Present	Duplicates onto a requested fd, closing it first.
pipe	Present	4 KiB ring with reader/writer refcounts.
fcntl	Partial	F_GETFL and F_SETFL; only documented bits are meaningful.
stat, fstat	Partial	Linux-shaped struct stat, limited fields, no permission enforcement.
readdir	Present	Makar-indexed syscall backing libc DIR * wrappers.

The VFS supports ISO9660, FAT32, ext2, tmpfs, devfs, procfs, and logfs. Not every filesystem supports every mutation. /tmp is the reliable scratch location during live boots. On a live-CD boot the elected rootfs is the read-only ISO9660, so the kernel overlays tmpfs at the home directories (/root, /home, /home/user) too — home writes (~/.mxrc etc.) succeed in RAM for the session, Ubuntu-live style; on an installed ext2/FAT32 root the real, persistent home is used. tmpfs is multi-instance (one namespace per mount), so these overlays never alias /tmp.

Memory APIs

Feature	Status	Notes
brk	Present	Main heap-growth mechanism for the userspace malloc shim.
mmap2	Anonymous + file-backed (RO shared)	Anon non-fixed = demand-paged bump window at 0x90000000. A read-only file map shares frames from the page cache (pagecache_acquire), so libc.so’s text/rodata is one copy in RAM across all mappers; writable/tmpfs file maps and anon-fixed take a private frame. Backs musl ld.so’s library maps.
munmap	Present	Unmaps the range and releases each frame (vmm_unmap_and_free, refcount-decrement — shared cache frames survive while others map them). Address reuse within the bump window is not implemented.
MAP_FIXED	Present	Maps at the caller’s exact address, replacing any existing mapping in that window.
mprotect	Present	SYS_MPROTECT (125) rewrites PTE R/W/USER over the range (ld.so RELRO). i386 non-PAE has no NX, so X is implicit.
executable mmap/JIT	Unsupported	TCC compiles to files and execs them; tcc -run is not the supported model.

Anonymous mmap exists because hosted libc allocators, including musl paths, expect it for larger allocations. The implementation is intentionally simple: zero-filled frames are mapped into a bump region and are not reused during the process lifetime.

Signals

Feature	Status	Notes
kill	Present	Sends a signal to a pid.
signal	Present	Installs a simple handler or disposition.
user handlers	Present	Delivered through a userspace sigframe and sigreturn.
default termination	Present	Fatal default signals mark the task dead.
sigreturn	Present	Internal trampoline syscall.
rt_sigprocmask	Stub	Returns success for hosted libc startup; real masking is not complete.
sigaction	Absent	Use signal for now.
sigsuspend, pause	Absent	No blocking signal-wait API.
process groups	Absent	No job-control signal model.

Signal support is good enough for current apps and tests (sigtest.elf) but not yet a complete POSIX signal subsystem.

Time

Feature	Status	Notes
gettimeofday	Present	Seconds from CMOS RTC; microseconds are PIT-derived at 10 ms resolution.
clock_gettime	Present	CLOCK_REALTIME and CLOCK_MONOTONIC.
time	Present	Userspace libc wrapper.
gmtime, gmtime_r	Present	Integer-only UTC conversion.
localtime, localtime_r	Present	Alias UTC; no timezone database.
mktime	Present	UTC interpretation.
strftime	Partial	Common numeric/date specifiers.
nanosleep	Absent	sleep/usleep spin-yield on the 250 Hz tick.

There is no locale or timezone database. Treat all broken-down time as UTC.

Floating Point

The kernel initializes the x87 FPU and enables FXSAVE/FXRSTOR where available. Each task has a 512-byte FPU state area, and the scheduler saves/restores it around context switches. Floating-point state is therefore multitask-safe.

What is still missing is the userspace libc surface: there is no shipped <math.h> implementation and no complete floating-point formatting/parsing library.

TLS and Hosted libc Startup

Both static and dynamically-linked i386 musl startup need a small Linux-compatible substrate. Makar now provides:

• a full System-V i386 ELF auxv: AT_PHDR, AT_PHENT, AT_PHNUM, AT_BASE, AT_ENTRY, AT_EXECFN, AT_RANDOM, AT_PAGESZ, AT_NULL
• set_thread_area(243) using one GDT TLS slot at selector 0x33
• %gs preservation across interrupts
• scheduler TLS restore for TLS-active tasks
• writev (musl’s buffered stdio writes through it)
• exit_group
• set_tid_address
• rt_sigprocmask stub
• ioctl returning -ENOTTY
• futex stub for the current single-threaded bring-up assumption

For dynamic linking the loader additionally honours PT_INTERP (/lib/ld-musl-i386.so.1, == libc.so), enters at the interpreter, and the kernel services musl’s ld.so runtime: file-backed/MAP_FIXED mmap2, mprotect (RELRO), and open returning -ENOENT so the library search walks.

These are compatibility pieces, not full Linux implementations. They exist to get hosted binaries through early libc initialization and dynamic relocation.

Userspace libc Headers

Header	Current coverage	Important gaps
<stdio.h>	FILE * I/O, printf family subset, fd-backed reads/writes	no wide char, no popen, incomplete buffering controls
<stdlib.h>	allocation, conversions, qsort, bsearch, env table, system, sscanf	env does not cross execve; no locale/multibyte family
<string.h>	memory/string basics, strtok, strtok_r, strerror	no collation/locale transforms
<unistd.h>	common declarations and thin wrappers: fd I/O, dup, pipe, pids, cwd, sleep	no alarm, pause; no POSIX fork/exec wrappers yet
<dirent.h>	opendir, readdir, closedir	backed by indexed syscall rather than Linux getdents
<errno.h>	common errno constants and global errno	not every syscall wrapper sets errno yet
<time.h>	UTC broken-down time and strftime subset	no timezone, no ctime/asctime/difftime
<setjmp.h>	i386 setjmp/longjmp	no signal-mask variants
<ctype.h>	ASCII C-locale classifiers	no locale
<math.h>	absent	FPU substrate exists, library does not
<pthread.h>	absent	no user threading

Shell Compatibility

The default interactive shell is /apps/sh.elf. It supports:

• variables and $?
• quoting with quote removal
• sh -c
• if, while, for
• [ ... ]
• pipelines
• redirection
• &&, ||
• background &
• wait

The in-kernel script interpreter is smaller. It is used for boot/test scripts and intentionally does not support pipes, redirection, list operators, or background jobs. Use /apps/sh.elf for scripts that need those features.

Known shell deviations:

• no command substitution
• no shell functions
• no case
• no subshell syntax
• no true job control
• $ expansion currently happens before tokenization, so single quotes do not fully suppress variable expansion

Terminal Model

Makar does not have a POSIX termios layer. Programs use Makar-specific syscalls for terminal size, cursor position, drawing, raw keyboard mode, and caret style. Virtual terminals and app tabs are managed through Makar VT extensions and makmux.

The tty command prints Linux-shaped names:

• /dev/console for the root console
• /dev/ttyN for VT slots
• not a tty for unbound tasks

App-Porter Checklist

When porting a small C program:

1. Prefer static builds.
2. Avoid threads.
3. Avoid file-backed mmap and mprotect.
4. Use /tmp for scratch writes during live boots.
5. Expect all local time to be UTC.
6. Avoid termios; use Makar terminal syscalls or simple stdio.
7. Prefer /apps/sh.elf if the program shells out through system.
8. Check both return values and errno; errno coverage is improving but not universal.
9. Run alloctest.elf, libc-tcc.sh, and shell-smoke.sh when adding libc surface.
10. Run kbtest when changing keyboard, VT, makmux, shell focus, or app-tab behavior.